The present invention relates to a technique for shaft-sealing a circumference of a rotary shaft of a compressor of an air-conditioner using a mechanical seal.
FIG. 6 is a view showing a typical example of a conventional mechanical seal used as a shaft-seal means of a compressor of an air-conditioner for automobile use (a car air-conditioner) in which CO2 gas is used as refrigerant. This type mechanical seal 200 is composed as follows. On the rotary shaft 101 of a gas compressor, the refrigerant of which is CO2 gas, the rotary side sliding ring 201 is arranged via the O-ring 202 in such a manner that the rotary side sliding ring 201 is capable of moving in the axial direction and rotating together with the rotary shaft 101. The stationary side sliding ring 203, which cannot rotate, is airtightly arranged via the O-ring 204 on the seal housing 102 side of the gas compressor, the refrigerant of which is CO2 gas. The rotary side sliding ring 201 is closely contacted with the stationary side sliding ring 203 by a pushing force generated by the spring 205 in the axial direction. When both the rings 201 and 203 are closely contacted with each other, the airtightly sealed sliding face 200S is formed.
In this case, space A in the device, which is located on the right in the drawing and reaches the outer circumference of the airtightly sealed sliding face 200S, is filled with an atmosphere of CO2 gas containing refrigerating machine oil. Space B on the atmosphere side reaches the inner circumference of the airtightly sealed sliding face 200S. The differential pressure xcex94p between space A in the device and space B on the atmosphere side changes in a range from 3 to 13 MPa. The rotary side sliding ring 201 is made of carbon sliding material having a self-lubrication property. The sliding protrusion 201a, which is continuously formed in the circumferential direction, of the rotary side sliding ring 201 is slidably contacted with the stationary side sliding ring 203. The stationary side sliding ring 203 is made of sliding material of ceramics which is harder than the carbon sliding material described above.
According to the conventional mechanical seal 200 described above, the rotary side sliding ring 201 made of carbon sliding material, the Young""s modulus of which is low, is deformed into a tapered-shape which is exaggeratedly shown in FIG. 7. The reason why the rotary side sliding ring 201 is deformed into a tapered-shape will be explained as follows. The rotary side sliding ring 201 is given a displacement force as shown by arrow xe2x80x9cfxe2x80x9d by the differential pressure xcex94p acting in the radial direction on a portion close to the stationary side sliding ring 203 with respect to the O-ring 202 which is arranged on an inner circumference of the rotary side sliding ring 201. Therefore, the portion of the rotary side sliding ring 201 close to the stationary side sliding ring 203 leans against the stationary side sliding ring 203 side. The sliding protrusion 201a, the bending strength of which is low from the viewpoints of profile and structure, further leans against the inner circumferential side by the differential pressure acting in the radial direction.
As a result, for example, in the case where a mechanical seal is used in which the rotary side sliding ring 201 is made of carbon sliding material, the outer diameter of the sliding protrusion 201a is approximately 20 mm and the width of the airtightly sealed sliding face 200S in the radial direction is approximately 2 mm, partial abrasion is caused by sliding in which the quantity of abrasion in the outer circumferential portion of the sliding protrusion 201a is larger than that in the inner circumferential portion of the sliding protrusion 201a by about 1 to 3 fm (femto-meter).
Therefore, when displacement force xe2x80x9cfxe2x80x9d caused by differential pressure xcex94p is reduced according to the reduction of gas pressure of refrigerant CO2 filled in space A in the device, as shown in FIG. 8, a tapered gap xe2x80x9cgxe2x80x9d, which is open onto the outer circumferential side (refrigerant gas CO2 atmosphere side) is caused due to the above partial abrasion. Accordingly, when differential pressure xcex94p acts on this gap xe2x80x9cgxe2x80x9d, an intensity of force OP to open the airtightly sealed sliding face 200S is increased.
When some refrigerating machine oil, which exists in the refrigerant gas CO2 in a mist form, is introduced onto the airtightly sealed sliding face 200S, an oil film is formed on the airtightly sealed sliding face 200S. The thus formed oil film greatly contributes to the prevention of leakage of refrigerant CO2 gas. When the tapered gap xe2x80x9cgxe2x80x9d, which is open onto the outer circumferential side as described above, is formed, the width of the airtightly sealed sliding face 200S is remarkably decreased, and the oil film existing on the tightly sealed sliding face 200S is remarkably decreased. Therefore, refrigerant CO2 gas tends to leak from the device.
The present invention has been accomplished to solve the above problems. The primary technical task of the present invention is to prevent the collapse of an oil film on the airtightly sealed sliding face and suppress the leakage of refrigerant gas caused by the collapse of the oil film when deformation of the sliding ring and sliding protrusion caused by the pressure in the space in the device is reduced and partial abrasion on the airtightly sealed sliding face, which is caused by the deformation, is reduced.
The above technical task can be effectively accomplished by the present invention.
The present invention provides a shaft seal mechanism of a compressor with a mechanical seal, the mechanical seal comprising: a rotary side sliding ring supported by an outer circumferential face on a large diameter side of an annular step section formed on a rotary shaft of a compressor via a rotary side packing, the rotary side sliding ring being press-fit into the annular step section by gas pressure in the compressor; and a stationary side sliding ring, which is not rotated, airtightly fixed onto a seal housing side of the compressor via a stationary side packing in such a manner that the stationary side sliding ring can be moved in the axial direction, the stationary side sliding ring airtightly coming into contact with the rotary side sliding ring by a pushing force of a spring in the axial direction so as to form an airtightly sealed sliding face, wherein a space in the compressor in which gas to be sealed exists reaches an outer circumferential side of the airtightly sealed sliding face, the rotary side sliding ring is made of a self-lubrication sliding material, the stationary side sliding ring is made of a sliding material, the Young""s modulus of which is higher that that of the self-lubrication sliding material, and a sliding protrusion extending from the rotary side sliding ring in the circumferential direction slidably comes into contact with the stationary side sliding ring. In this case, the self-lubrication sliding material, which is material of the rotary side sliding ring, is a carbon sliding material, a PTFE sliding material or a polyimide sliding material.
In the above structure, the rotary side sliding ring is given a deforming force in the leaning direction by a differential pressure between high gas pressure in the device and atmospheric pressure outside the device, however, this deforming force is canceled by a deforming force generated by a component force in the axial direction of the differential pressure acting on the annular step section of the rotary shaft in a pushing direction. Therefore, the occurrence of partial abrasion of the airtightly sealed sliding face, which is caused by a deformation of the rotary side sliding ring by leaning, can be suppressed. In this connection, the stationary side sliding ring is also given a deforming force in the leaning direction by the differential pressure in the same manner as that described above. However, since this stationary side sliding ring is made of material, the Young""s modulus of which is high, a quantity of deformation is very low, which causes no problems.
A more preferable structure to be added to the present invention is described below. A gap in the axial direction is formed in an outer circumferential section between an annular step section of the rotary shaft and a back face of an inner diameter section of the rotary side sliding ring, which are contacted with each other, being located on the inner diameter side with respect to an airtightly sealed section formed by the rotary side packing. Due to the foregoing, a deforming force, the direction of which is opposite to that of the deformation of the rotary side sliding ring by leaning, is generated. Therefore, the occurrence of partial abrasion on the outer circumferential side of the airtightly sealed sliding face caused by the deformation by leaning can be more positively prevented.
The present will be more easily understood from the following descriptions of embodiments with reference to the accompanying drawings.